Electric arc furnace (EAF) steelmaking is a highly energy-intensive industrial process. It consumes a large amount of electrical and chemical energy. A modern EAF produces over 300 tapping tons of steel pear heat, and since the production of steel in an EAF requires a huge amount of electrical and chemical energy, the energy cost for one such furnace annually is very high. This is the reason why the latest EAF technology development has been mainly focused on reducing the energy consumption (electricity and oxygen) and thereby increasing the productivity. Also from an environmental point of view there is a desire to reduce the emissions of carbon dioxide and other emissions from the EAF.
A typical electric arc furnace comprises three electrodes, a power supply system operatively connected to the electrodes, a vessel, often water-cooled in larger sizes, covered with a retractable roof through which one or more graphite electrodes enter the furnace. Further an electric arc furnace usually comprises a cooling water station and at least one control unit operatively connected to the power supply system to control the operation of the electrodes. The electrodes form an arc between the metallic material (e.g. scrap), which has been loaded into the EAF, and the electrodes. Thereby, a metallic melt (a charge) is created which is heated both by current passing through the melt and by the radiant energy evolved by the arc. An electrode regulating system maintains approximately constant current and power input during the melting of the charge.
Arc furnaces usually exhibit a pattern of hot and cold-spots around the hearth perimeter, with the cold-spots located between the electrodes. Modern furnaces mount gas burners in the sidewalls and use them to provide chemical energy to the cold-spots, making the heating of the melt more uniform. Additional chemical energy is also provided by means, e.g. lances, for injecting oxygen and carbon into the furnace.
A typical EMS-system comprises at least one electromagnetic stirrer comprising a stirring coil, a power supply system, comprising frequency converter and a transformer, operatively connected to the stirrer, a cooling water station and at least one control unit operatively connected to the power supply system to control the operation of the stirrer. The stirring coil is typically mounted outside a steel shell of the furnace. This coil generates a travelling magnetic field to provide stirring forces in the melt of molten metal. The stirrer operates using a low frequency travelling magnetic field, penetrating the steel shell of the furnace and thereby moving the melt.
US 2004/244530 A1 discloses a method of controlling slag characteristics in an electric arc furnace control. The furnace has inputs including oxygen supply and carbon supply. The method of controlling slag characteristics includes introducing a charge to be melted into the furnace, melting at least a portion of the charge to produce a melt, and introducing oxygen and carbon into the melt to enhance formation of a slag having slag conditions including a slag height and a slag coverage. To better control the slag characteristics, the slag is modeled and the inputs are controlled to maximize the energy transferred from the electrode to the slag.
US 2007/133651 A1 discloses a method for controlling the foaming of slag in an electric arc furnace. The furnace comprises at least one electrode column. Current is applied to the electrode column, causing an arc to form between the tip of the electrode column and the scrap, melting the scrap. Impurities in the molten scrap metal rise to the surface forming slag. A meter determines the total harmonic distortion associated with the system. If the total harmonic distortion is greater than a predetermined set point, and the scrap metal is sufficiently molten, then a foaming agent is added thereto.
The publication “Tenova's intelligent arc furnace iEAF—concept and technical overview” by Clerci et al., published in Steel Times International, DMG World Media, Lewes, G B, vol. 32, no. 4, 1 May 2008, pp. 19-23, discloses an automation system based on continuous, real-time process measurements and online process models, developed for the dynamic control and optimization of the electric arc furnace.